IE43610B1 - Multi-core optical communications fibre - Google Patents
Multi-core optical communications fibreInfo
- Publication number
- IE43610B1 IE43610B1 IE1504/76A IE150476A IE43610B1 IE 43610 B1 IE43610 B1 IE 43610B1 IE 1504/76 A IE1504/76 A IE 1504/76A IE 150476 A IE150476 A IE 150476A IE 43610 B1 IE43610 B1 IE 43610B1
- Authority
- IE
- Ireland
- Prior art keywords
- wave
- fibre
- optical
- guiding
- core
- Prior art date
Links
- 230000003287 optical effect Effects 0.000 title claims abstract description 39
- 239000000835 fiber Substances 0.000 title claims abstract description 35
- 238000004891 communication Methods 0.000 title claims abstract description 28
- 239000013307 optical fiber Substances 0.000 claims abstract description 20
- 238000000034 method Methods 0.000 claims abstract description 15
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 20
- 239000000463 material Substances 0.000 claims description 14
- 239000000377 silicon dioxide Substances 0.000 claims description 9
- 238000012544 monitoring process Methods 0.000 claims description 7
- 230000001902 propagating effect Effects 0.000 claims description 7
- JKWMSGQKBLHBQQ-UHFFFAOYSA-N diboron trioxide Chemical compound O=BOB=O JKWMSGQKBLHBQQ-UHFFFAOYSA-N 0.000 claims description 6
- 229910052810 boron oxide Inorganic materials 0.000 claims description 5
- YBMRDBCBODYGJE-UHFFFAOYSA-N germanium dioxide Chemical compound O=[Ge]=O YBMRDBCBODYGJE-UHFFFAOYSA-N 0.000 claims description 5
- 239000004033 plastic Substances 0.000 claims description 4
- 229920003023 plastic Polymers 0.000 claims description 4
- 239000011521 glass Substances 0.000 claims description 3
- 238000005253 cladding Methods 0.000 description 23
- 230000005540 biological transmission Effects 0.000 description 3
- 229910011255 B2O3 Inorganic materials 0.000 description 1
- 238000005229 chemical vapour deposition Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 230000001960 triggered effect Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/80—Optical aspects relating to the use of optical transmission for specific applications, not provided for in groups H04B10/03 - H04B10/70, e.g. optical power feeding or optical transmission through water
- H04B10/85—Protection from unauthorised access, e.g. eavesdrop protection
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02042—Multicore optical fibres
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/44—Mechanical structures for providing tensile strength and external protection for fibres, e.g. optical transmission cables
- G02B6/4439—Auxiliary devices
- G02B6/4469—Security aspects
Landscapes
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- General Physics & Mathematics (AREA)
- Computer Security & Cryptography (AREA)
- Optics & Photonics (AREA)
- Electromagnetism (AREA)
- Signal Processing (AREA)
- Computer Networks & Wireless Communication (AREA)
- Optical Communication System (AREA)
- Light Guides In General And Applications Therefor (AREA)
- Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)
- Glass Compositions (AREA)
- Burglar Alarm Systems (AREA)
Abstract
Methods and apparatus are disclosed for providing a multipath optical communications system within a single fiber. One embodiment comprises a concentric multi-core optical fiber having an inner core for transmitting information and an outer core for transmitting a security signal. Attempted access to the inner core causes a decrease in the security signal intensity alerting the operator to the attempted intrusion.
Description
The advent of optical fibres for communication purposes was first lought to provide ready means for transmitting secret information without elaborate >curity precautions. Access to the information was considered impossible since ie fibre would have to be broken in the process. Several ingenious methods for lining access to the fibre core without breaking the fibre have evolved since ie first early optical communication systems were devised.
One method for gaining access to information transmitted within the bre core consists of etching away a portion of the optical cladding material and upling into the light path by submersing the fibre in a material of high refractive dex. By this method light can be caused to be transmitted from the fibre core rough the high index of refraction material where it can be optically received d monitored. Methods have been proposed for encoding the information data in der to preserve the system’s security, but the use of complex encoding equipment d circuitry at the optical transmitter end, and the use of similar decoding apparatus the optical receiver end adds to the large quantity of communications equipment iloyed within the optical communication system.
According to the present invention there is provided an optical fibre ’ing a first wave-guiding structure extending within and completely surrounded by a ond wave-guiding structure, wherein the parameters of the fibre are such that the each propagating mode of the first wave-guiding structure is not appreciably pled with any propagating mode of the second wave-guiding structure.
A multiple core optical fibre enables secure - 2 43610 Information transmission by transmitting the secret information within an inner core and transmitting a security signal through an outer core. An intervening cladding layer of lower index material prevents any appreciable intermixing between the -secret information and the security signal. Attempted access to the inner core causes a decrease in. the intensity of the security signal to alert an operator to the attempted intrusion.
There follows a description of a communications system using a multi-cored fibre embodying the invention in a preferred form. 'The description refers to the accompanying drawings, in which:Figure 1 is a cross-section of a concentric multiple core optical fibre, Figure 1Λ shows the multiple core fibre of Fig. 1 consisting of four cores; Figure 2 is a block diagram of an optical communications system using the fibres of Fig. 1? and Figure 3 is an alternative embodiment of the system of Fig. 2.
Fig. 1 is a cross-section of the concentric multicore fibre 1 which can be made by standard optical fibre processing techniques.
One method for forming the multi-core fibre consists in the successive application of a number of layers of material by the process known as chemical vapour deposition. Here alternate layers of high and low index of refraction material are deposited on the inner surface of a silica tube. The material contributing to the higher index region may be germania-silica glass, for example, and the material - 3 43610 contributing to the lower index of refraction boron oxide doped silica glass. The higher index regions may have the same index of refraction, but this is not necessary.
Another method for forming the multi-core fibre of this invention involves the insertion of a number of concentric cylinders within an outer silica tube. The cylinders are alternately of high index material, such as germania-silica, and low index material such as the boric oxide· doped silica glass as described above.
A further method for providing the multiple core fibre of this invention is simply to surround a glass optical fibre, having a germania Silicate core, a boron oxide doped silica cladding and a silica outer tube, with an outer cladding layer of low index plastic. The silica, having a higher index of refraction than both the boron oxide doped silica /glass and the-plastics cladding layer, presents an annular that waveguiding structure / surrounds the central waveguiding which structure /comprises the boron oxide doped silica cladding surrounding a germania doped silica core.
) A further method for forming the concentric multicore fibre of this invention is to alternately deposit successive high and low index of refraction plastic material.
, The fibre consists of a central core herein designated as a signal core of a material having an index of refraction n4· An inner cladding layer of an index of refraction n^ completely encloses the signal core for confining light energy Within the signal core by the method of complete internal refraction since n^ is chosen less than n^. The combination of the signal core of refractive index n^ and the inner cladding layer of refractive index n2 constitutes an optical fibre similar to the optical fibre of the prior art, Λ second core designated as an alarm core is concentrically applied over both the inner cladding and the signal core, and consists of a material of an index of refraction n2 which is slightly higher than the refractive index of the inner cladding n^. The alarm core is surrounded by an outer cladding layer having a refractive index v/hich is slightly less than the refractive index n2 of the alarm core. Light energy transmitting through the alarm core will be confined within the core since the inner cladding laying and outer cladding layer have lower indexes of refraction (η^, np than the index of refraction of the alarm core n2· The signal core and the alarm core are optically independent from each other provided that the intervening inner cladding layer of lower refractive index n^ is thick enough, in which case they can be considered as two separate and parallel light conduits. Light from one source can therefore travel through the signal core, and light from an independent source can travel through the alarm core with no appreciable interference or intermixing between the two light signals. The required thickness of the intervening cladding is that which separates the cores to the extent that the presence of either core acts as no more than a second order perturbation upon the modes associated with the other core. The actual value of the required thickness depends inter alia upon the refractive index.difference between the cladding and the cores. Typically when this difference is about 1%, adequate separation may be provided by a cladding thickness of a - 5 ~ few tens of wavelengths so long as the fibre quality Is good» Tho presence of imperfections and scattering, centres is liable to introduce mixing between the two sets of modes.
The concentric dual core described in Fig. 1 can be used to transfer secret information in the following manner. A modulated light signal carrying secret information can be directed through the signal core to a remote receiver at an opposite end of the multi-core fibre. Light from a separate source could be transmitted through the alarm core to another receiver at the opposite end of the cable. When an intruder attempts to tunnel through the outer cladding layer and through the alarm core, in an attempt to gain optical access to the signal core, the light output received through the alarm core at the opposite end of the fibre will significantly diminish in intensity. This is brought about by the fact that the outer cladding has been at least partially removed in the process so that light normally reflected in toto from the cladding will leak out through the discontinuity in the outer cladding layer. Light passing through the alarm core will become obstructed by the presence of any implement passing through the light path consisting of the total area of the alarm core region. Light passing through the alarm core will also pass through the discontinuity in the inner cladding layer which provides ah optical boundary between the' alarm core and signal core for the reasons stated earlier.
Fig. 2 shows an optical communications system where the signal core region of the fibre described in Fig. 1 is designated analagously as a communications signal path 4, and the alarm core region of the same fibre is designated as a security signal path 2. The security signal path 2 tind the signal communications path 4 arc described as separate light paths fo.r the purpose of clarity only since they actually have the cross-sectional, configuration shown in Fig. 1. A first optical transmitter 10 generates an information modulated light signal having the direction of arrow .1.6 v/hich passes through the signal communications path 4 to an optical receiver 12. This is analagous to the transmission of secret information from an independent light source through tha signal core of the inventive fibre of Fig. 1. A second optical transmitter 6 generates a security light signal having the direction of arrov/ 14 through the security signal path 2 where it is received by a second optical receiver 8. The security signal path 2 is analagous to the alarm core region of the aforementioned fibre of Fig. 1. While the secret information is being transmitted through the signal communications path 4 the security signal is constantly being monitored for intensity in the optical receiver 8. When a decrease is observed in the light output of the security signal at receiver 8 the operator of the optical transmitter 10 should immediately be informed of the possibility of an attempted intrusion into the security signal path 2.
• In the optical communications path of Fig. 3 the same signal core region and alarm core region of the inventive fibre of Fig. 1 are designated by the communications signal path 4 and security signal path 2 as for the system of Fig. 2. Here the direction of travel between the security signal path designated by arrow 7 is opposite to that of the signal communications path designated by arrow 5. In this embodiment the optical transmitter 10 transmitting secret Information along the communications signal path 4 to the optical receiver 12 simultaneously receives a security signal from a second optical transmitter S by means of the second optical receiver 6. In this embodiment the operator of transmitter 10 in close proximity to receiver 6 immediately observes a decrease in the security signal originating at the second optical transmitter 8 and passing through security signal path 2. Here the operator Of transmitter 10/ upon learning of the possible attempted intrusion through the alarm core of the fibre herein designated as Security signal path 2, could then intentionally transmit erroneous information or alternatively close down transmission.
Various electro-optical devices can be employed in order to cause an automatic shut-down in the transmitter 10 upon a decrease in the-light intensity of the security signal arriving at the receiver 6.
In the operation of such a system the operator of transmitter 10 may first send .a request for a security signal from the operator of transmitter 8, to which the operator of transmitter 8 replies by sending a pre-arranged security signal through the security signal path 2 to optical receiver 6. The aforementioned operator of optical transmitter 10 would then know that the communications signal path 4 is clear for transmitting secret information. After sending the secret information through signal path 4 and by continuously monitoring the intensity of the security signal at receiver S, observation of a decrease in the intensity at receiver 6 would be indicative of an attempt by an intruder to gain access to the secret - 8 43620 information as described earlier.
Tiie concentric multiple core fibre shown in Fig. 1 can have several layers of signal cores and alternate layers of alarm cores or, alternatively, could have a series of signal cores side by side each carrying separate information along distinct optical paths which are enclosed by one encompassing alarm core for providing security to all the signal cores contained within the fibre. A fibre having several concentric and independent cores is shown, for example, in Fig. IA.
Although the concentric core fibre and security optical communications system have herein been described for secret information purposes, such as military communications, this is by way of example only and is not to be considered in any way as a limitation on the scope of this invention. The invention finds application in all types of optical communications systems where means for determining attempted intrusion upon the signal are required. One such application, for example, is in telephone communication systems utilizing optical fibre telephone lines. When an attempt is made to tap the telephone line, by removing the outer cladding to gain optical access into the inner information carrying core, it may be arranged that the parties at both ends of the telephone line are immediately made aware of the attempted intrusion by the operation of an alarm triggered by a monitoring system at the receiver end of the security signal path.
Claims (14)
1. An optical fibre having a first wave-guiding structure extending within and completely surrounded by a second wave-guiding structure wherein the parameters of the fibre are such that the or each propagating mode of the first wave-guiding structure·is not appreciably coupled with any propagating mode of the second waveguiding structure.
2. An optical fibre as claimed in Claim 1 wherein at least one other idditional wave-guiding structure extends alongside the first wave-guiding structure vithin and completely surrounded by the second wave-guiding structure and wherein she parameters of the fibre are such that the or each propagating mode of the or >.ach additional wave-guiding structure is not coupled with any propagating mode >f the second wave-guiding structure. !.
3.An optical fibre as claimed in Claim 1 wherein at least one other dditional wave-guiding structure extends within and completely surrounded by the econd wave-guiding structure wherein all of said wave-guiding structures are arranged oncentrically and wherein the parameters of the fibre are such that the or each ropagating mode of the or each additional wave-guiding structure is not coupled ith any propagating mode of the second wave-guiding structure. .
4.An optical fibre as claimed in Claim 1 s 2 or 3 wherein at least one f the wave-guiding structures is formed at least in part by germania doped silica. ' .
5.An optical fibre as claimed in Claim 1, 2, 3 or 4 wherein at least one ’ the wave-guiding structures is formed at least in part by boron oxide doped ilica.
6.An optical fibre as claimed in any preceding claim wherein each wavetiding structure is formed by one or more interfaces across which there is a tractive index difference and wherein there is the same refractive index difference ross each of the interfaces of two or more of said wave-guiding structures.
7.An optical fibre as claimed in any preceding claim wherein at least rt of one of the wave-guiding structures is made of glass. -104361ο
8. An optical fibre as claimed in any preceding claim wherein at least part of one of the wave-guiding structures is made of a plastics material.
9. An optical fibre as claimed in Claim 1 and substantially as hereinbefore described with reference to Figures 1 or la of the accompanying drawings.
10. An optical communication system employing an optical fibre as claimed in any preceding claim wherein information is transmitted along said first waveguide structure to a first receiver and a monitoring signal is transmitted along said second wave-guide structure to a second receiver.
11., An optical communication system as claimed in Claim 10 wherein the 10 second receiver includes means for continuously monitoring the intensity of the received monitoring signal.
12. An optical communication system as claimed in Claim 10 or 11 wherein the information is transmitted along the fibre in one direction and the monitoring signal is transmitted in the opposite direction. 15
13. An optical communication system as claimed in Claim 10 or 11 wherein the information and the monitoring signal are both transmitted in the same direction along the fibre.
14. A method of transmitting information data in an optical communications system wherein optical communication is established through the first wave-guide 20 structure of an optical fibre as claimed in any claim of Claims 1 to 9 and wherein optical energy is transmitted along the second wave-guide structure of said fibre, the amount of which transmitted optical energy is monitored to determine any increase in optical attentuation suffered by said second wave-guide structure.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/595,247 US4000416A (en) | 1975-07-11 | 1975-07-11 | Multi-core optical communications fiber |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| IE43610L IE43610L (en) | 1977-01-11 |
| IE43610B1 true IE43610B1 (en) | 1981-04-08 |
Family
ID=24382419
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| IE1504/76A IE43610B1 (en) | 1975-07-11 | 1976-07-07 | Multi-core optical communications fibre |
Country Status (12)
| Country | Link |
|---|---|
| US (1) | US4000416A (en) |
| JP (1) | JPS5238238A (en) |
| AU (1) | AU502543B2 (en) |
| CA (1) | CA1087891A (en) |
| CH (1) | CH607064A5 (en) |
| DE (1) | DE2628561A1 (en) |
| ES (1) | ES449730A1 (en) |
| FR (1) | FR2317670A1 (en) |
| GB (1) | GB1543242A (en) |
| IE (1) | IE43610B1 (en) |
| NL (1) | NL7607538A (en) |
| ZA (1) | ZA763885B (en) |
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| US3535017A (en) * | 1968-01-08 | 1970-10-20 | Bell Telephone Labor Inc | Optical fiber waveguide structures |
| US3700900A (en) * | 1969-02-06 | 1972-10-24 | Arne J Herleikson | Dual purpose transmission line |
| US3636473A (en) * | 1969-03-06 | 1972-01-18 | American Optical Corp | Composite glass laser rod |
| US3583786A (en) * | 1969-09-23 | 1971-06-08 | Bell Telephone Labor Inc | Optical waveguide formed of cylinders with optically smooth interfaces therebetween |
| JPS4927233A (en) * | 1972-07-03 | 1974-03-11 | ||
| US3778132A (en) * | 1972-10-06 | 1973-12-11 | Bell Telephone Labor Inc | Optical transmission line |
| GB1422956A (en) * | 1972-11-10 | 1976-01-28 | Bicc Ltd | Optical guides |
| GB1456371A (en) * | 1972-11-25 | 1976-11-24 | Sumitomo Electric Industries | Optical transmission fibre |
| US3884550A (en) * | 1973-01-04 | 1975-05-20 | Corning Glass Works | Germania containing optical waveguide |
| JPS5535683B2 (en) * | 1973-08-10 | 1980-09-16 | ||
| US3980390A (en) * | 1974-03-20 | 1976-09-14 | Sumitomo Electric Industries, Ltd. | Optical transmission fiber |
-
1975
- 1975-07-11 US US05/595,247 patent/US4000416A/en not_active Expired - Lifetime
-
1976
- 1976-06-15 GB GB24682/76A patent/GB1543242A/en not_active Expired
- 1976-06-25 DE DE19762628561 patent/DE2628561A1/en not_active Withdrawn
- 1976-06-30 ZA ZA763885A patent/ZA763885B/en unknown
- 1976-07-05 AU AU15589/76A patent/AU502543B2/en not_active Expired
- 1976-07-07 IE IE1504/76A patent/IE43610B1/en unknown
- 1976-07-08 CH CH875876A patent/CH607064A5/xx not_active IP Right Cessation
- 1976-07-08 FR FR7620872A patent/FR2317670A1/en active Granted
- 1976-07-08 NL NL7607538A patent/NL7607538A/en not_active Application Discontinuation
- 1976-07-09 CA CA256,670A patent/CA1087891A/en not_active Expired
- 1976-07-09 ES ES449730A patent/ES449730A1/en not_active Expired
- 1976-07-12 JP JP51082059A patent/JPS5238238A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| IE43610L (en) | 1977-01-11 |
| GB1543242A (en) | 1979-03-28 |
| ES449730A1 (en) | 1977-12-16 |
| US4000416A (en) | 1976-12-28 |
| CA1087891A (en) | 1980-10-21 |
| DE2628561A1 (en) | 1977-01-27 |
| AU502543B2 (en) | 1979-08-02 |
| JPS5621121B2 (en) | 1981-05-18 |
| FR2317670A1 (en) | 1977-02-04 |
| FR2317670B1 (en) | 1982-04-02 |
| ZA763885B (en) | 1977-05-25 |
| JPS5238238A (en) | 1977-03-24 |
| NL7607538A (en) | 1977-01-13 |
| AU1558976A (en) | 1978-01-12 |
| CH607064A5 (en) | 1978-11-30 |
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